Urinary bladder and sphincter responses to stimulation of dorsal and ventral sacral roots.

The sacral spinal roots have a long intraspinal yet extradural pathway that makes them ideal for electrode implantation for the control of micturition. In the hope of identifying a specific motor pathway to the bladder within these roots, a study of 10 mongrel female dogs was undertaken: bladder and sphincter responses to stimulation of individual sacral roots, and to stimulation of the dorsal and ventral components of each root, were recorded urodynamically. The root producing greatest detrusor response was then divided into its motor and sensory components, and the central and peripheral ends of the latter were stimulated. We found that sphincter resistance to bladder emptying was diminished by removing the afferent dorsal roots from the stimulus field. The physiologic implications of this finding are discussed.